This invention relates generally to acoustic transducers having a piezoelectric bimorph structure and more particularly, it relates to an improved Helmholtz acoustical system which includes a tunable rear Helmholtz chamber and a tunable, front outer enclosing chamber both disposed within a single cavity so as to provide loud sound levels over a wider audio frequency range.
As is generally known, there exists in the prior art acoustic transducers which utilize piezoelectric elements suitably bonded to a support structure mounted in a singular specially-tuned cavity, as is shown in FIG. 1a. This is typically referred to as a single Helmholtz design wherein a piezoelectric crystal 2 mounted on a brass plate 4 is used to form the rear wall of a chamber 6. There is also known in the prior art acoustic transducers which have piezoelectric elements suitably bonded to a support structure mounted in dual specially-tuned cavities, as is shown in FIG. 1b. This is generally referred to as a dual Helmholtz design wherein a piezoelectric crystal B mounted on a brass plate 10 is used to separate first and second chambers 12, 14. While the single Helmholtz designs do offer relatively high sound levels, they suffer from the disadvantage of having a narrow bandwidth. The existing dual Helmholtz systems do offer a wider bandwidth, but this is achieved only at the expense of difficult assembly and through bulky designs for coupling the first and second chambers to a front radiating area.
It would therefore be desirable to provide an improved acoustical system for generating loud sound levels having a wider bandwidth. The acoustical system of the present invention represents an improvement over the existing singular and dual Helmholtz designs. The present acoustical system includes a tunable rear Helmholtz chamber coupled to a tunable front, outer enclosing chamber both disposed within a single cavity.